Motor fuels and processes for making same



Patented Aug. 27, 1946 fUNlTED STATES oFncs 2,406,667 l MOTOR FUELS AND Princesse FOR MAKING Ilouis A. Clarke, Fishkill, Y., assignor to The Texas Company, New York, N. Y., a corporation of Delaware No Drawing.

Original application July 23, 1942,

Serial No. 452,061. Divided and this application April 27, 1943, Serial No. 484,765

My invention relates to improved fuels for internal combustion engines, and to methods for producing and utilizing such fuels.

In the past, motor fuels have generally been rated on the basis of their performance. under relatively lean mixture'operating conditions. .This has resultedfrom considerations of fuel economy in the operation of automotive engines, and test methods such as the CFR octane number determinations have been devised accordingly. More.-

over, most fuels have .somewhat better anti-knock characteristics under rich mixture operating conditions, i. e., air-fuel ratios of about 12/ 1, than under lean mixture operating conditions, i.e., airfuel ratios of about 15/ 1. In the usual automotive engine, air-fuel ratios of less than 12/1 have been of no interest, since the use of such mixtures has resulted in both loss of power and loss of economy, 6

In the operation of supercharged engines, on the other hand, and especially those of high speed, high heat load types, the performance of I fuels in'mixtures richer than 12/lbecomes important. With such engines, the maximum power output at full throttle, without detonation, is obtainable only with super-rich mixtures, i. e., with air-fuel ratios less than ll/ 1, and usually considerably below /1. In order to obtain maximum power output from an aircraft engine for takeoff under heavy load, it is desirable to employ a fuel having anti-knock characteristics especially suited for operation at such super-rich mixtures.

It has been found that various fuels differ markedly in their performance in super-rich mixture, even though their anti-knock characteristicsat leaner mixtures may be substantially iden tical. Certain of the aromatic hydrocarbons such as benzene and toluene, when incorporated in a motor fuel, have been found to have the characteristic of considerably improving the fuel ini S performance in super-rich mixtures, although often at a considerable sacrifice offlean mixture performance. On the other hand,- the aliphatic hydrocarbon anti-knock standard, 2,2,4-trimethylpentane, does not have this property ofpreferentially improving the super-rich mixture performance of base fuels to which it is added; :and the paraffin hydrocarbons have generally been recognized to be lacking in thedesired superior performance in super-rich mixtures; f

I have now found; however, that 2,3-dimethy1- teristics in operation at air-fuelratios of less than .11/1, and is especially useful inthe formulation 3 Claims. (Cl. 44,8 0.)

forb'othlean and super-rich mixture operation, a

fuel comprising essentially this hydrocarbon could beemployed for all purposes. However, additional fuel constituents of higher and lower volatility than 2,3-dimethylbutane will usually be desirable for the productionlof a balanced fuel. Furthermore, for economic reasons it will usually not be desirable to employ a fuel consisting essentially of 2,3-dimethylbut'ane, since satisfactory performance can usually'be obtained by the use of somewhat less expensive fuel stocks in conjunction with 2,3-dimethylbutane. Fuels comprising essentially 2 ,3-dimethylbutane will, therefore, be of most value as auxiliary fuels, to be blended with,

or to be employed in conjunction with, other fuels which do not have satisfactory performance in super-rich mixtures. 7

As an auxiliary fuel, 2,3-dimethylbutane, or a solution having a relatively high concentration of 2,3-dimethylbutane, may be substituted for the primary fuel for operation at maximum power output, or may be blended with the primary fuel 'at times of increased power demands on the enoperation.

gine. In the former case, the fuel supply may suitably be changed manually, as in changing from a take-off fuel to-a cruising fuel in aircraft Where the auxiliary fuel is to be blended with the main fuel at times of increased power demand on the engine, this is preferably accomplished by an automatic blending device such as that described in U. S. Patent 2,002,482

:of Leo B. Kimball. Other equivalent methods for butane possesses outstanding anti-knock characemploying the auxiliary fuel may also be used,

such as supplying it to, an auxiliary carburetor 'jet with functions onl at full throttle. In any case, theair-fuel ratio..should be manuallyor .lauto'matically reducedfltb'a value below 11/ 1 when the'auxiliary, fuel 'isfsu'pplied to the engine, in order to obtain increased power output.

. Although it will usually be most economical to employ 2 +dimethylbutane as, an auxiliary fuel only at times of increased power demands on the engine, it will often be most practical to employ only a single fuel having satisfactory anti-knock characteristics in both lean mixtures and superrich mixtures. For this purpose, a base fuel is chosen which has satisfactory performance in lean mixtures, and 2,3-dimethylbutane is incorporated in the fuel in an amount sufficient to improve the performance of the fuel in super-rich mixtures. Any amount which produces a measurable improvement may be employed, but I usually prefer to use at least by volume, and preferably 20-30% or more, depending upon the anti-knock characteristics of the base fuel, and on the character and amount of any additional anti-knock agents employed.

The base fuels with which 2,3-dimethylbutane may be employed, either in blended mixtures or in separate auxiliary fuels, may be any of the known types of motor fuels for internal combustion engines. Straight run gasolines, thermally or catalytically cracked gasolines, polymer gasolines, alkylation gasolines, thermally or catalytically reform d or hydroformed gasolines, and various blends of such products are suitable for the present purpose. Base fuels which are especially desirable are those having high power output in lean mixtures, such as fuels containing relatively large amounts of 2,2,4-trimethylpentane. ,The alkylate from the hydrogen fluoride alkylation of isobutane with isobutylene, as described in my co-pendin application, Ser. No. 429,471, filed February 4, 1942, and the hydrogenated dimer from the cold acid polymerization of isobutylene, are especially suited for this purpose.

The base fuels and auxiliary fuels, or the blended fuels, may all contain additional antiknock additives and other common fuel constituents such as gum inhibitors, agents for scavenging metallic engine deposits, and the like. The anti-lmock properties of 2,3-dimethylbutane in super-rich mixtures are-especially advantageous in fuels containing other anti-knock components. Although different types of anti-knock materials in admixture often produce much less than additive results, the preferential improvement in super-rich mixtures produced by 2,3- (limethylbutane appears to be at least additive with the effects of other anti-knock components such as tetra-ethyl lead. It is to be understood, therefore, that one aspect of my invention constitute the use of 2,3-dimethylbutane in conjunction with any of the known anti-knock additives such as tetra-ethyl lead, iron pentacarbonyl, aromatic hydrocarbons, or aromatic amines.

Although various chemical syntheses may be employed for the production of 2,3-dimethylbutane, one of the most economic sources is the alkylation of isobutane with ethylene, using an aluminum halide catalyst as disclosed in my copending application Ser. No. 439,299, filed April 17, 1942. The pure compound, 2,3-dimethylbutane, may be recovered from such alkylation products by fractional distillation, if desired. However, the over-all alkylate, or a relatively wide-boiling cut containing 2,3-dimethylbutane, may be used as the auxiliary fuel in the present invention, or for blending with other base fuels to improve their performance in super-rich mixtures. l

The rich mixture performance of 2,3-dimethylbutane is illustrated in the following examples:

Example I gallon, in accordance with the AFB-3C test method. At an air-fuel ratio of approximately -10.5/1 the permissible indicated mean effective pressure (IMEP without detonation) was 259 lbs/sq. in. This corresponded to the maximum power output which could be absorbed by the test engine dynamometer, but the trend of the measured values of IMEP indicated that the fuel would be capab-le of much greater power output in still richer mixtures. In a comparable test in the same engine, commercial 2,2,4-trimethy'lpentane plus 6 ml. of tetra-ethyl lead per gallon produced a permissible IMEP of only approximately 221 lbs./sq. in. at an air-fuel ratio of 10.5/1 and a maximum permissible IMEP of only 249 lbs/sq. in. at an air-fuel ratio of approximately 8/ 1.

Example II A fuel consisting of 75% by volume of commercial 2,2,4-trimethylpentane and 25% by volume of 2,3-dimethylbutane, plus 3 m1. of tetraethyl lead per gallon, was tested by the AF'D BC method. The maximum permissible IMEP was found to be 2 13 lbs/sq. in. at an air-fuel ratio of approximately 10.5/1. In a comparable test in the same engine, commercial 2,2,4-trimethylpentane plus 4 ml. of tetra-ethyl lead per gallon gave a maximum permissible IMEP of only 233 lbs/sq. in.

Example III A fuel consisting of by volume of a debutanized 300 F. end-point alkylation gasoline (from the sulfuric acid alkylation of isobutane with butylenes) and 20% by volume of 2,3-dimethylbutane, plus 3 ml. of tetra-ethyl lead per gallon, was tested by the AFB-3C method. The maximum permissible IMEP was found to be 218 lbs/sq. in. at an air-fuel ratio of approximately 8.5/l, as compared to a maximum permissible IMEP for debutanized alkylate, plus 3 ml. of tetra-ethyl lead, of only approximately lbs/sq. in. At a lean mixture (air-fuel ratio of approximately 14.3/1) the permissible IMEP values for these two fuels were 111 lbs/sq. in. and 95 lbs/sq. in., respectively.

Comparable tests with the same alkylation gasoline, leaded to the extent of 4 ml. of tetraethyl lead per gallon, with and without ethylbenzene for improving the super-rich mixture performance, are shown in the table below:

Max. IMEP, lbs ./sq.

Lean IMEP (fuel/air= 0.07)

Change in max. IMEP Change in lean IMEP Fuel composition 20% ethylbenzene 227 97 4.0 ml. TEL/gal As may be seen from the above table, 23- dimethylbutane is superior to ethylb'enzene for improving the performance of thisalkylation gasoline in super-rich mixtures without sacrificing lean miXture'performance.

This application is a division of application of Louis A. Clarke, Serial No. 452,061, filed July 23, 1942, for Motor fuels and processes for making and utilizing same. Said application Serial No. 452,061 is a continuation-in-part of application of Louis A. Clarke, Serial No. 439,299, filed April 17, 1942, which in turn is a continuation-in-part of applications, Serial No. 324,784, filed March 19, 1940 and Serial No. 327,575, filed April 3, 940.

It is to be understood, of course, that the above examples are merely illustrative, and do not limit the scope of my invention. As has previously been pointed out, other constituents may be employed in blended fuels containing 2,3-dimethylbutane, and such fuels may be formulated in accordance with prior practices in the art, except for the improvement in super-rich mixture operation effected by the incorporation of 2,3-dimethylbutane. It should also be understood that 2,3-dimethylbutane is especially adapted for use in conjunction with all other types of anti-knock additives such as aromatic hydrocarbons, aromatic amines, and other organo-metallic anti-knock agents, as well as the particular materials employed in these examples. In general, it may be said that the use of any equivalents, or modifications of procedure which would naturally occur to those skilled in the art, is included in the scope of this invention. Only such limitations as are indicated in the appended claims should be imposed on the scope of my invention.

I claim:

1. An aviation fuel blend adapted for use in supercharged engines and having a preferentially improved maximum power output at full throttle, without detonation, at super-rich air-fuel ratios richer than 11:1, as compared with lean air-fuel ratios leaner than 11:1, comprising a high antiknock rating base fuel containing a major proportion of isoparaffinic hydrocarbons and an antiknock additive, and a blending fuel comprising 2,3-dimethylbutane in major proportion by volume of the blending fuel, the latter being added in sufficient proportion to include at least 10%- 30% by volume of 2,3-dimethylbutane in the base fuel and sufficient to convert the base fuel into the aforesaid aviation fuel blend.

2. An aviation fuel blend adapted for use in supercharged engines and having a preferentially improved maximum power output at full throttle, without detonation, at super-rich air-fuel ratios richer than 11:1, as compared with lean air-fuel ratios leaner than 11:1, comprising a high antiknocl: rating base fuel containing a major proportion of isobutane-butylene alkylate gasoline and an anti-knock additive, and a blending fuel comprising 2,3-dimethylbutane in major proportion by volume of the blending fuel, the latter being added in a proportion to include at least 10 %-30% by volume of 2,3-dimethylbutane in the base fuel and suflicient to convert the base fuel into the aforesaid aviation fuel blend.

3. An aviation fuel blend adapted for use in supercharged engines and having a preferentially improved maximum power output at full throttle, Without detonation, at super-rich air-fuel ratios richer than 11:1, as compared with lean air-fuel ratios leanerthan 11:1, comprising a high antiknock rating base fuel consisting essentially of a debutanized aviation fraction of alkylation acid catalyzed isobutane-butylene alkylate and an anti-knock additive, and a blending fuel consisting essentially of a wide-boiling cut of aluminum chloride catalyzed isobutane-ethylene alkylate containing a major proportion by volume of 2,3-

dimethylbutane, said blending fuel being added in a proportion to include at least 10%-30% by volume of 2,3-dimethylbutane in the base fuel and sufficient to convert the base fuel into the aforesaid aviation fuel blend.

LOUIS A. CLARKE. 

